Electron tube circuits



April 7, 1953 P. N. MAR-N 2,634,385

ELECTRON TUBE CIRCUITS Filed Aug. 24, 1948 7b AL. Uonr'ol 3 Source.

7b 1.6. Some.

IN VEN TOR.

ail! M MqPlh.

Patented Apr. 7, 1953 UNITED STATES PATENT OFFICE ELECTRON TUBE CIRCUITS Paul N. 'Martin, Penn Township, H Allegheny county, Pa", ass'ignor to Westinghouse Air Brake col'npan'y, a corporationof Pennsylvania Application August 24, 1948, Serial No. 45,937

1 Claim;

My invention relates to electron tube circuits and particularly to electron tube circuits arranged to provide safe operation of'the circuits and apparatus associated therewith.

For the purposes of this disclosure, it is to be understood that the term electron tube shall mean an electron discharge device comprising an enclosure containing therein two or more electrodes and being either highly evacuated or filled with gas at a low pressure, while the term gas tube shall specifically "mean an electron tube filled with gas at a low pressure.

In certain applications of electron tube circuits such as, for example, relay control circuits for railway signaling systems, it is essential to insure that the relay governed by the electron tube will pick up when and only when a control voltage of particular character is supplied to the input circuit of the electron tube which has the relay winding connected to its anode circuit. .A bias voltage is generally provided for preselecting the operating characteristics of the electron tube circuits, and it is necessary to provide means for checking the continuity of the elements by which the bias voltage is supplied to "the tube.

Additionally, it has been found that under certain conditions electron tubes of the gas type will continue to conduct, having once been rendered conductive, if the input circuit to the .grid and cathode oi the tube is interrupted in such manner that the grid is coupled, capacitively or otherwise, to a possible source of stray voltage.

Another possible cause or improper operation of tube circuits is that of .false firing or conduction of the tube due to leakage of current in the tube base or wiring between the anode and control grid when the normal input circuit between the contrdl grid and cathode of the tube is interrupted.

Accordingly, it is anobject of my invention to provide novel and improved electron tube circuits arranged for safe operation.

Another object of mylinvention is toprovide electron tube circuits incorporating novel means for checking the supply of bias voltage to an electron tube. V

A further object of my invention isto provide electron tube circuits incorporating novel means for preventing the conduction of the tube by leakage current if the control circuit therefor becomes disconnected-.

Another object of my invention is to provide novel and improved electron tube circuits arranged to prevent the conduction of the tube by stray Voltages supplied to the grid ofth tube if'the' g-rid c'athode circuit interrupted;

Other objects of my invention'and features of novelty thereof will be apparent from the following description taken in connection with the accompanying drawings.

In practicing my invention I provide a circuit arrangement which includes one or more of the control electrodes in a multi-element electron tube and the source of bias voltage in series with the anode circuit of the tube, and also includes the control circuit for the tube in series therewith, so that the several circuits form a series arrangement, whereby an interruption or" any part of the complete circuit prevents the flow of current in the anode circuit and thereby prevents the operation of the relay in the anode circuit 'of the tube. Additionally, I provide a fourterminal condenser connected in shunt across the input circuit in order to shunt stray voltages while the plates of the condenser are connected as series elements in the input portion of the circuit so that an open connection to the condenser results in a safe failure of the apparatus.

I shall describe two forms of apparatus embodying my invention and shall then point out the novel features thereof in the claim.

.In the accompanying drawings,

Fig. 1 is a diagrammatic view showing one-form of electron tube circuits embodying my invention when employing a four-element electron tube,

and

Fig. 2 is a diagrammatic view showing a modification of the arrangement of Fig. 1, which employs a three-element electron tube.

Similar reference characters refer to similar parts in each of the two views.

Referring to Fig. 1, the reference character VTI designates a four-element indirectly heated gas tetrode of the thyratron type, having an anode 5, a shield grid 7, a control grid 9, a cathode II and a heater i3. The shield grid 1 of tube VTI is provided with two terminals l5 and I1, and the control grid 9 is also provided with two terminals I9 and 2|, and these grids are arranged so that the grid structure forms a series circuit between the terminals associated with each of the grids. Thus a circuit connected to the terminals of these grids includes the grid structures and grid connections in series so that any break in the grids or their connections within the tube will interrupt the circuit. The heater l3 of tube VTI is supplied with energy from a suitable source, not shown.

Power is supplied to the anode 5 of the tube VTI from a suitable source, here shown as a secondary winding SI having terminals 25 and 27 of a transformer PT, which has its primary acegsss winding P connected to a suitable source of alternating current, not shown. A second secondary winding S2 provided with terminals 2s and 3!, provides a suitable source of bias voltage for the shield grid 3 of the tube VTl. The winding of a relay R and a limiting resistor RP are connected in series between terminal 25 of secondary winding 5! and the anode 5 of tube VTI, and terminal 2'! of secondary winding Si is connected to terminal l5 of the shield grid Relay R is of the type having contacts which are slow to release, in order that the contacts of the relay will remain picked up during the alternate half cycles of the alternating current supplied to the anode circuit of the tube for which the tube is non-conductive, and the slowreleasing feature is preferably secured by the use of a copper ferrule or sleeve on the core of the relay, which acts as a short-circuited single turn winding, this type of relay structure reducing the value of induced voltage generated by the self-induction of the winding of the relay when the current which flows therethrough is cut oil.

.A contact 33 of relay R governs a control circuit, not shown.

Terminal 1? of shield grid 7 of the tube VT! is connected to terminal 3! of the secondary winding S2 through a current limiting resistor RS, and terminal 29 of the secondary winding S2 is connectedto terminal 26 of the control grid Q of tube VTi.

The the VT! is governed by a source of alternating current control energy, not shown, which energy is at times supplied to the primary winding 35 of a control transformer CT. The secondary winding 3'! of control transformer CT is provided with'terminals 39 and ll, and terminal 39 is connected to terminal it of the control grid 9 of tube VTI by'a circuit which includes in series a grid resistor RG and one plate of a four-terminal condenser C, this one plate having terminals 43 and 45. Terminal dl of the secondary winding of transformer CT is connected to the cathode ll of tube VT! by a circuit including in series the other plate of condenser C, and which other plate is provided with terminals ll and 49.

These several circuits of tube VT! are connected in series to form an anode circuit which may be traced from terminal 25 of secondary winding Si of transformer PT through resistor RP, through the winding of relay R to the anode 5 of tube VTl, through the tube space'of tube VTi to the cathode H, through one plate of condenser C by way of terminals ii} and i? to the terminal il of secondary winding 3? of transformer CT, from the other terminal 39 of secondary winding 37 of transformer CT through the other plate of condenser C by way of terminals 33 and 55, through the limiting resistor RG, through control grid 9 of tube V'Ti by way of terminals i9 and 2i to the terminal 28 or" the secondary winding S2 of transformer PT, from the other terminal 3i of secondary winding S2 .through the limiting resistor RS, and through the shield grid l of tube VIl by way of terminals l! and IE to the terminal 2's of secondary winding S5 of transformer PT. Accordingly, it will be seen that during the half cycles of alternating current energy supplied by the secondary winding Si, in which the terminal 25 is positive in polarity with respect to the terminal 2?, ii the bias voltage and the control voltage are suitable to cause the tube to conduct, current flows through the circuit traced above to energize relay R and causes the contact 33 of relay R to be picked up. As previously explained the relay R is slow in releasing, so that during the alternate half cycles in which the tube VT! is nonconductive, the relay R will continue to hold its front contact 33 closed.

The conducting condition of tube VTi is predetermined by the proper arrangement and proportioning of the bias voltage supplied to the shield grid 7 of tube VTi from the secondary winding S2 of transformer PT. The bias voltage supplied to the shield grid l from the transformer PT is supplied thereto by a circuit one side of which may be traced from terminal 31 of secondary winding 52 through the limiting resistor RS to terminal i? of the shield grid 5, and the other side of which circuit may be traced from the terminal 29 of secondary S2 to the cathode ll of tube VTl through the control grid 9, by way of terminals 2! and E9, the limiting resistor RG, one plate of condenser C by way of terminals s5 and 43, the secondary winding 37 of control transformer CT by way of terminals 29 and ll, and to the cathode ll of tube VTl through the other plate of condenser C by way of terminals nl'i and 49. The windings Si and S2 of transformer CT are arranged and connected so that the energy supplied to the anode of the tube and the bias voltage supplied to the shield grid of the tube are of opposite polarity. That is, when the instantaneous polarity of the alternating current energy supplied from the secondary windings Si and S2 is such that the anode 5 of tube VTl is positive with respect to the cathode l i, the biasing voltage supplied from the secondary winding S2 is such that the shield l is negative with respect to the cathode li.

From the foregoing, it will be seen that the circuit network shown in Fig. l is arranged and constructed so that the circuit by which energy is supplied to the winding of relay R includes in series therewith all other elements of the circuit network, so that if a break develops in any portion of the circuit network, the supply of energy to the relay R will be interrupted, and its contact 33 will release, opening the circuit which is controlled thereby. The secondary windings "SI and S2 are proportioned and ar= ranged so that normally, that is, when no control voltage is supplied to the control grid 9, the bias voltage supplied to the shield grid 1 of tube V'll is sufficient to prevent the tube from firing during the alternate half cycles in which the anode E is positive with respect to the cathode ll.

It will now be assumed that a control voltage of proper phase and voltage value is supplied to the primary winding 35 of control transformer CT. Accordingly, a potential is established between the control grid 9 and the cathode, ll of connection with tracing the anode circuit. If

the polarity of the alternating current control voltage supplied at this time is such that the control grid 9 is positive with respect to cathode ll of tube VTl at the time during which the anode '5 is also positive with respect to the cathode H, and if the control voltage supplied to the control grid 9 of tube VTI is of sumcient value to overcome the biasing voltage applied to the shield grid 1, the tube will conduct and energy will be supplied to the winding of relay R and its contact 33 will be picked up. As previously explained, during the alternate half cycles in which the trol voltage is supplied to the polarity-ofthe voltage supplied to the anode 50f tube VTI is negative, so that the tube cannot conduct, the relay R will remain picked up due to its slow releasing characteristics. Thus, it will be seen that when control voltage of the proper value and phase relationship to the voltage is supplied to the-anode and the screen grid 1 of tube VTI, the relay Rwill be energized and itscontact 33 will be picked up and remain picked up as long as the alternating current conprimary winding 350i transformer CT.

As previously explained, the circuit for supplying energy to the winding of relay R includes theshield grid "land the control grid 9, the secondary winding $2, the secondary winding 31 of transformer CT and the plates of conden'serC in axserieszcircuit. Accordingly, ifany :portion of .the'circuit .is broken, .whether the gridsbecome openinside the tube,.-or if the wire connection between: the various elements becomes broken or disconnected, it will. be apparent that the supply of energy to thewinding of relay R will be interrupted, so that contact 33' of relay R will release after aztime interval,,,and will remain released. Also, if the supply of bias voltage is interrupted in such manner thatthe tube -might possibly conduct without thepresence of a positive potential on the control grid 9, t-he anodecircuit will -be-open,and relay R will be released, Likewise ,7

if anyof the elements in the control portion of the circuit including the secondary winding 3'! of:transf,ormer CT, the condenser C, and their connections to the control grid 9 and cathode H becomeopen, the anode circuit including relay R will be interrupted, so that relay R will release.

From the foregoing, it will be seen that vacuum tube circuits arranged as shown in Fig. 1 will provide safe operation, and the derangement of any portion of the circuits will be promptly detected by the failure of the relay R to pick up, which in itself is a failure on the side of safety.

In the types of electron tube circuits previously proposed, if the connection between the source of control voltage and the cathode of the tube became open while the connection between the control source and the control grid remained intact, stray high-frequency voltages supplied to the grid of the tube by capacitive coupling effect :were in some cases sufficient to cause the tube to become conductive. However, in a circuit arranged asshown in Fig. 1 and embodying my in- 'vention,'I provide condenser C, which is proportioned and arranged to effectively shunt any such stray voltages which are present in the input circuit including the secondary winding 31 of transformer CT. It is contemplated that the condenser C will be selected so that it will have suflicient reactance at the frequency of the control voltage to prevent it from shunting the control energy enough to prevent the tube VTI from being properly controlled thereby, but that the condenser C will have suificient capacity to effectively shunt small stray high-frequency voltages which may appear across the secondary winding 31, due to extraneous voltages supplied from the alternating current control source. In order that the presence of condenser C may be checked at all times to insure that stray voltages supplied from the secondary winding 31 will be shunted, the plates of the condenser are each provided with two terminals, and the anode circuit is carried through each plate of the condenser as previously traced. Accordingly, it will be seen that if either plate of condenser C becomes open or if the connections thereto-are open or brokemthe anode circuit will be interrupted, so that relay R will release if pickedup or remain releasedif not picked up.

Since the circuit for supplying the alternating current control voltage to the control grid 9 of tube VTI isa portionof the series anode circuit previously described, it will be apparent that should the connection to the control grid 9 become broken ordisconnected, the .anode circuit for the tube will be interrupted so that relayR will-be released if already pickedup or will fail to pick up. Accordingly, no possibility of 'false firing of thetube due to leakage between the anode 5 or its connections and the control grid 9 orits connections can occur since any such leakage current will be shunted by the relatively low impedance winding 31 and capacity C, as long as'the circuit is intact, so that such leakage current will not develop appreciable voltage between the control grid and cathode sufficient tocause the tube to fire improperly. If the grid circuit connection to capacity C'and-winding 37 is open,

the anode circuit will also be interrupted at the same point as previously pointed out.

The grid protective orlimiting resistor RG, which is included primarily to limit theflow of currentbetween the grid and cathode when the control grid is at positive potential, mayalternatively be connected between the control source and capacitor C, that is, between terminals 39 and Y43. The capacitor 0 would thus be even more effective in shunting stray high-frequency voltages from the control grid.

Invacuum tube circuits of the type described it has been the practice to provide a relay which is rendered slow in releasing its contactsby the connection of a condenser, resistor, or a snubbing rectifier across the winding of the relay. Such an arrangement may result in false operation of the relay, since if the snubbing circuit becomes disconnected, the inductivevoltage provided by the self-induction of the relay winding when the anode circuit is interrupted may be sufficient to cause the tube to remain in a conductive condition and thus cause the relay'to remain picked up. Accordingly, I prefer to provide arelay of the type which is rendered-slow in releasing by the provision of acopper ferrule or sleeve surrounding the core structure of the relay, since the possibility of a short or open circuit in this single-turn copper winding is extremely remote.

Referring to Fig. 2, there is showna modification for the arrangement shown in Fig. 1, in which the tube VTZ is a three-element indirectly heated gas triode. The parts are arranged and constructed in the same manner as those shown in Fig. 1, with the exception that the biasing voltage supplied by the secondary winding S2 of transformer CT is utilized to provide a negative potential on the control grid 9 of the tube VTZ, so that during the time that the anode voltage is positive wtih respect to the cathode, the biasing voltage supplied to the control grid 9 will prevent the tube from conducting.

The anode circuit for the tube VTZ including the winding of relay B, may be traced from terminal 25 of secondary winding SI of transformer PT, through the resistor RP and the winding of relay R to the anode 5 of tube VTZ, through the tube space to the cathode I l of the tube, to terminal 29 of the secondary winding S2 of transformer PT, from terminal 3| of secondary winding S2 through one plate of condenser C by way of 7 terminals 49 and 41, through the secondary winding 3! of the control transformer CT by way of terminals M and 39, through the other plate of condenser C by Way of terminals 43 and 45 to the resistor RG, and through the control grid 9 of tube VTZ by way of terminals [9 and 21 to terminal 2'? of the secondary winding SI of transformer PT. As explained in connection with Fig. 1, the anode circuit includes all of the con- .trol elements in a series arrangement, so that an interruption in any portion of the circuit willinterrupt the supply of energy to the winding of relay R. The secondary winding $2 of transformer PI is arranged and constructed to provide a biasing voltage to the control grid 9 of tube VTZ which is sufiicient to prevent the'tube from becoming conductive during the alternate :half cycles in whichthe anode 5 of tube VTZ is positive with respect to the cathode ll. Accordingly, during the time in which there is no control energy supplied to the primary winding 35 of the control transformer CT, the tube remains non-conductive and the contact 33 of relay R is released.

If an alternating current control voltage is .now applied to the primary winding 35 of the control transformer CT, the alternating current voltage induced in the secondary winding 31 of transformer CT will be supplied to the grid 9 of tube VTZ, and if this voltage is of sufficient value to overcome the biasing voltage supplied from the secondary winding S2 of transformer CT, the tube will conduct on alternate half cycles, and the relay R, will pick up its contact 33. As explained in connection with Fig. 1, the

relay R. is slow in releasing so that contact 33 remains picked up during the alternate half cycles in which the tube is not conducting.

As explained in connection with Fig. 1, the

anode circuit of the arangement shown in Fig.

2 is a series arrangement in which all of the control elements and the sources of energy for the operation of the tube are checked. Accordingly, if one of the connections is broken or the series circuit is otherwise interrupted, the supply of energy to relay R will be interrupted and after a short time interval its contact 33 will release. As previously explained, the release of contact 33 of relay R is considered a safe type of failure.

From theforegoing, it will be seen that my invention provides electron tube circuits in which all of the elements are checked by a series circuit arrangement, and which series circuit includes the relay controlled by the electron tube, so that any failure of a portion of the circuit will'result in the relay being deenergized.

Although the circuits have been shown and described as employing gas type tubes of the thyratron type, it is to be understood that my invention is not limited to this type of tube, and any suitable type of electron tube may be used.

Although I have herein shown and described only two forms of electron tube circuits embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention, claim is:

In combination, an electron tube of the gas type having an anode, a cathode and a control electrode; said tube provided with two terminals between which said control electrode forms a series path, an anode voltage source, a bias voltage source, a condenser, the plates of which are provided each with two terminals and between which two terminals the respective plate forms a seriespath, a control winding to which a control voltage is at times applied, and a circuit including in series said anode voltage source, said anode and tube space to said cathode, said bias voltage source, one plate and its two terminals of said condenser, said control winding, the other plate and its two terminals of said condenser, and said control electrode with its two terminals;

whereby false firing of said tube due to a broken circuit element of said bias voltage source or of said control winding or of said condenser is avoided.

PAUL N. MARTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

